In general, an LED lighting device includes an inrush current limiting circuit to limit an inrush current flowing through a capacitor for smoothing a power source voltage or an output voltage of a switching circuit when a power is turned on. Further, in the LED lighting device, the inrush current limiting circuit is set to an operation state suppressing the current flowing therethrough at an initial stage of turning on the LED lighting device, and then set to a non-operation state not suppressing the current flowing therethrough when a predetermined switching circuit of the LED lighting device is operated.
In case where the LED lighting device includes a plurality of switching circuits, the predetermined switching circuit may not be started first. In this case, the inrush current limiting circuit is maintained in the operation state until the predetermined switching circuit is operated, and thus an input current to the LED lighting device is limited.
Accordingly, the LED lighting device may supply a current enough to operate the switching circuits thereof, and thus the switching circuits may not perform desired operations. The desired operations are, e.g., supplying a desired output power from the switching circuit and the like.
FIG. 6 illustrates a circuit configuration of a conventional LED lighting device including an input filter 2 connected to a power source 1, a rectifying circuit 3, switching circuits of a step-up chopper circuit 7 and a step-down chopper circuit 9, an inrush current limiting circuit 5, and a control circuit 13.
The power source 1 is an AC power source. The step-up chopper circuit 7 includes a MOS-FET Q11, a primary winding (represented by a) of a transformer T11, a first (input side b) secondary winding of the transformer T11, a diode D11, and a resistor R11. The transformer T11 is formed of coils.
The step-down chopper circuit 9 includes a MOS-FET Q12, a primary winding (represented by a) of a transformer T12, a first (input side b) secondary winding of the transformer T12, a diode D12, a resistor R12, and a capacitor C12. The transformer T12 is formed of coils.
The inrush current limiting circuit 5 includes a resistor R13 serving as an inrush current limiter, a switching element Q13, a capacitor C12, resistors R14 and R15, diodes D13, and a second (output side c) secondary winding of the transformer T11. (see Japanese Patent Application Publication Nos. H5-257548 and S60-51415)
In the LED lighting device shown in FIG. 6, a trigger signal of the operation/non-operation of an inrush current limiting circuit 5 is supplied from the step-up chopper circuit 7. In this case, if the step-down chopper circuit 9 is started first after a power source 1 is turned on, the input current flows through a resistor R13 of the inrush current limiting circuit 5 until the step-up chopper circuit 7 is operated.
Accordingly, the LED lighting device shown in FIG. 6 may not accumulate a sufficient amount of electric charges in a smoothing capacitor C11 located at the output of the step-up chopper circuit 7 by consumption of the input current due to the step-down chopper circuit 9 and a voltage generated across the resistor R13.
That is, in the LED lighting device shown in FIG. 6, the output of the step-up chopper circuit 7 may not have a desire voltage.